Mounjaro and Wegovy: Are They the Same Medication?

Different drugs, different mechanisms: what the approvals actually say

Mounjaro contains tirzepatide, made by Eli Lilly. Wegovy contains semaglutide, made by Novo Nordisk. They belong to related but distinct pharmacological classes. Semaglutide activates one receptor, the GLP-1 receptor, mimicking a gut hormone that promotes fullness and slows gastric emptying. Tirzepatide activates two receptors simultaneously (GLP-1 and GIP) making it the only dual-agonist weight-loss medicine currently licensed in the UK. The practical significance of that second pathway is still being studied, but the MHRA's separate licensing decisions for each product reflect that these are genuinely different molecules with different clinical profiles.

Both carry a Black Triangle (▼) on UK labelling, meaning the MHRA collects additional safety data on an ongoing basis. Both are prescription-only and are licensed for adults alongside a reduced-calorie diet and increased physical activity. Neither is a substitute for the other without prescriber input, if you've been reading about whether Wegovy and Mounjaro are the same thing, the short answer is that they are not, even though the comparison is understandable given how similarly they're discussed in the press.

One routine difference worth knowing: Mounjaro is stored in the fridge at home (some people keep theirs in the fridge door alongside everyday items) but the exact room-temperature window for each pen differs between products, so always check the Patient Information Leaflet or the relevant Summary of Product Characteristics on the eMC rather than relying on general guidance.

What the phase-3 trial results show, and where the head-to-head data sits

The two medicines have been studied in separate landmark programmes. SURMOUNT-1, published in the New England Journal of Medicine, followed 2,539 adults over 72 weeks; participants on the highest tirzepatide dose achieved an average weight reduction of around 20–21%, with some analyses reaching approximately 22.5%. The STEP 1 trial, also published in the New England Journal of Medicine, enrolled adults on semaglutide 2.4mg over 68 weeks and found an average reduction of roughly 15%.

Those figures come from separate trials with different populations, so a direct numerical comparison has limits. The cleaner evidence comes from SURMOUNT-5, a head-to-head open-label trial of 751 adults with obesity and no diabetes, run over 72 weeks. It found that tirzepatide produced a greater average weight reduction than semaglutide 2.4mg, findings that informed NICE's appraisal of tirzepatide (TA1026). The gap narrows with Wegovy's newer 7.2mg dose, approved by the MHRA in January 2026, which reported around 20.7% average weight loss over 72 weeks, approaching tirzepatide's higher-end results.

For anyone curious about the relationship between semaglutide and Mounjaro more broadly, the distinction is the same: semaglutide is the active ingredient in Wegovy, not in Mounjaro.

Side-effect profiles: similar territory, some differences in detail

Both medicines share a broadly GI-led side-effect profile. Nausea, loose stools, constipation, indigestion, burping and fatigue appear in the trial data for each. These effects are typically most noticeable after starting treatment or after a dose increase, and for most people they ease within a week or two as the body adjusts.

There are some clinically relevant differences in how they interact with other medicines. For tirzepatide specifically, women taking oral contraceptives are advised to add a non-oral method of contraception during the first four weeks of treatment and for four weeks after each dose increase, because the absorption of the pill may be reduced. NHS England advises considering transdermal HRT forms for the same reason. Current guidance does not flag the same interaction risk for semaglutide, though your prescriber will review your full medication list regardless.

On safety monitoring more broadly, the MHRA issued a Drug Safety Update in January 2026 flagging acute pancreatitis as a known but infrequent serious risk across GLP-1 medicines, severe abdominal pain that radiates to the back warrants prompt medical attention. This applies to both products. You can report any suspected side effect from either medicine through the MHRA's Yellow Card scheme.

Eligibility and the clinical choice between them

NICE recommends tirzepatide (TA1026) for adults with a BMI of 35 or above alongside at least one weight-related comorbidity; NICE recommends semaglutide (TA875) under stricter conditions, specifically within a specialist weight management service and for a maximum of two years. Both recommendations include lower BMI thresholds for certain ethnic backgrounds. The licensed criteria for private prescription follow the SmPCs rather than NHS commissioning rules, so the conversation with a prescriber is broader than the NHS access criteria alone.

A detailed side-by-side breakdown of the clinical considerations is on our Wegovy vs Mounjaro comparison page, and the NICE appraisal of tirzepatide is readable in full at NICE TA1026. Which medicine is appropriate for a specific person is a clinical judgement, not a popularity contest. Our prescribers work through exactly that question with every patient.

If you'd like to explore the cost side of this comparison, our page on tirzepatide versus semaglutide costs in the UK covers the pricing landscape honestly. And if questions remain about whether these treatments overlap in other ways, our page covering whether Wegovy and Mounjaro are the same goes into that question in detail, as does the Wegovy v Mounjaro page. Which suits you is a clinical decision our prescribers make with you, not one a webpage can settle.